1. Technical Field
This invention relates to a method and apparatus for shipping, storing and freezing super frozen perishable materials in a self-contained container which maintains the perishable material below −50 degrees C. using its own cryogenic-based refrigeration system.
2. Background Information
Commercial fishing is a worldwide enterprise generating billions of dollars in sales on an annual basis. With modern shipping and storage technology, fish caught nearly anywhere in the world can be efficiently frozen and subsequently transported to almost any market in the world for consumption thereof.
Particular products however, do not lend themselves to conventional freezing and shipping methods. In particular, fish intended for consumption in an uncooked or raw state such as sushi, generally cannot be frozen using conventional equipment, without adversely affecting the quality, i.e., color and taste thereof. For this reason, fish intended for use as sushi generally must be caught locally so it can be brought to market relatively quickly without freezing. This necessity has tended to limit the supply of fish available for sushi to effectively increase the price thereof relative to frozen fish. This phenomenon tends to produce a relatively large disparity between the price of sushi-grade fish and non-sushi grade (i.e., frozen) fish in the marketplace.
In a recent attempt to address this disparity, some commercial fishing enterprises have harvested fish, such as tuna and the like, in areas of the world where there is little local demand for sushi-grade product (and thus a substantially lower market value therefor), and transported the product at cryogenic (i.e., super-cooled) temperatures of less than −40 degrees C. to the sushi markets. It has been found that at these temperatures tuna and the like maintain suitable freshness for sushi purposes to thus retain the relatively high quality and premium prices associated with sushi-grade product. This approach has generally required dedicated use of cargo ships known as super carrier vessels, outfitted with specialized refrigeration equipment specifically designed to maintain a constant cryogenic temperature of about −60 degrees C. The expense of such vessels typically dictates their use only when a substantially full shipment of approximately 100 metric tons (100,000 kilograms) or more of product is available for shipment. Accordingly, in order to satisfy this relatively high minimum volume requirement, such ships must generally remain at port or in the vicinity of tuna fishing fleets for extended periods of time as the fish are harvested and prepared for shipment. Disadvantageously, this aspect generally limits the number of trips from the fishing ports to the sushi markets to approximately one or two trips per year. For many perishable products this high volume requirement and low trip frequency renders this approach impractical. For many products which are in demand, the time required for shipment on a super carrier vessel, often several months from harvest to arrival at the destination, further makes such a shipping method undesirable.
Smaller shipments of conventionally frozen (i.e., 0 to −26 degrees C.) product have been shipped utilizing standard ISO containers on conventional transport ships. These ISO containers are relatively plentiful and the conventional transport ships travel on a relatively frequent basis to most desired destinations. These containers are typically refrigerated by use of mechanical refrigeration units associated with each individual ISO container. These refrigeration units, however, have not been capable of providing refrigerated temperatures of less than about −25 degrees C. Moreover, such mechanical units are prone to mechanical failure, in which about 5 to 10 percent of shipments are lost due to spoilage primarily due to mechanical breakdown and human error. Such units are also relatively expensive, generally costing on the order of $8000 to $10,000 for the container, an additional $10,000 to $12,000 for each refrigeration unit plus another $10,000 to $12,000 for an electric generator (i.e., genset) to provide electric power for the refrigeration unit. A further drawback of these mechanically refrigerated containers is that they generally must be transported on ships equipped for “reefer” (i.e., refrigerated) shipments, i.e., on ships capable of providing a continuous supply of fuel and/or electricity to the containers and including technicians capable of servicing the units in the event of a failure en-route. Shipping rates for such reefer containers tend to be considerably higher than rates for “dry” containers (i.e., those not requiring such services) of comparable size and weight.
Other conventional refrigerated transportation devices include ISO containers which are filled with product and injected with liquid gas (such as CO2) to form dry ice which maintains the product in a frozen state for the duration of the transport. A drawback of this approach, is that most such containers have generally been unable to maintain product at the aforementioned cryogenic, super-frozen temperatures. Rather, such containers, which utilize CO2 and the like, have been used to ship standard frozen products which only require refrigeration to approximately −10 degrees C. Although the dry ice has a frozen temperature of approximately−50 to −60 degrees C., such containers generally provide an oscillating temperature environment during shipment. For example, fresh product is typically loaded into a container and liquid CO2 is then injected to form dry ice at about −78 degrees C. at sea level. The dry ice thus gradually freezes the product bringing the product temperature from ambient temperature down to about−40 to −50 degrees C. until the CO2 has sublimated at which time the product begins to increase in temperature during transport. The duration of the shipment is timed so that the container arrives at the destination before the product temperature exceeds about −10 degrees C. This approach thus provides an oscillatory, rather than the desired steady state shipment temperature.
Examples of such devices include Carbon Dioxide Refrigeration Systems (U.S. Pat. No. 3,695,056: Glynn; E. P. and Hsu; H. L.), Refrigeration system with carbon dioxide injector (U.S. Pat. No. 4,399,658: Nielsen; D. M.), Container CO2 cooling system (U.S. Pat. No. 4,502,293: Franklin Jr.; P. R.), Liquid nitrogen freezer (U.S. Pat. No. 4,580,411: Orfitelli; J. S.), Portable self-contained cooler/freezer apparatus for use on common carrier type unrefrigerated truck lines and the like (U.S. Pat. No. 4,825,666: Saia, Ill; L. P.), Refrigerated container (U.S. Pat. No. 4,891,954: Thomsen; V. E.), Portable self-contained cooler/freezer apparatus for use on common carrier type unrefrigerated truck lines and the like (U.S. Pat. No. 4,991,402: Saia, III; L. P.), Portable self-contained cooler/freezer apparatus for use on airplanes, common carrier type unrefrigerated truck lines and the like (U.S. Pat. No. 5,125,237: Saia, III; L. P.), Self-contained cooler/freezer apparatus (U.S. Pat. No. 5,262,670: Bartilucci; A.), Portable self-contained cooler/freezer apparatus with nitrogen environment container (U.S. Pat. No. 5,598,713: Bartilucci; A. R.).
All of the above apparatus are characterized by the ability to cool or freeze perishable material down to about the temperature of approximately −20 degrees C. This is adequate and even desirable for some applications. However, for materials that require super freezing at temperatures of approximately −60 degrees C. such apparatus are unable to fulfill the requirements. The inability of the aforementioned apparatuses to maintain the super frozen temperatures is exacerbated by their use of two separate compartments. In this regard, the first of these compartments typically contains the perishable material, while the second of these compartments contains the cooling agent (CO2 or N2). Cooling is accomplished by the cooling agent moving from the second to the first compartment via a venting system.
The aforementioned U.S. Pat. No. 6,003,322 (the '322 patent) was able to achieve the desired superfrozen temperatures, in part by depositing the cooling agent (e.g., CO2 snow) directly on the product, for enhanced heat transfer from the product to the refrigerant. However, the snow covering the product tends to be an encumbrance for personnel working in the container. Moreover, the gaseous form of the cooling agent, e.g., CO2 sublimated from CO2 snow must be removed from the cargo compartment prior to entry by workers. This gas is not easily reclaimed and thus this greenhouse gas is generally released into the environment rather than being recycled for future use.
It is thus desirable to provide a device and method for enabling shipment of product in conventional bulk shipping containers on board conventional shipping vessels at a steady state super-frozen temperature, without the need for enabling the cooling agent to enter the compartment containing the product.